Background:
Colorectal carcinoma (CRC) is the third most frequent malignancy
worldwide. Over 30 years, the core therapy of CRC remains
5-fluorouracil (5-FU). Only 1–3% of administered 5-FU is converted
into its active form – fluorodeoxyuridine monophosphate.
Several studies indicate potential prognostic and predictive role
of 5-FU metabolizing enzymes in resistance of CRC. This study
focused on involvement of fifteen 5-FU pathway genes in the
prognosis of CRC patients.

Material and
Methods: Testing set and two validation sets consist of
paired tumor and non-neoplastic control tissue samples from 154 CRC
patients and were used for transcript and methylation profiling.
Gene expression of 15 genes was performed using quantitative
real-time PCR and methylation profiling was performed using high
resolution melting analysis. These molecular profiles were then
correlated with clinical data of patients. Further, most relevant
candidate markers were chosen and their protein profile was
assessed by immunoblotting.

Results: In
testing and validation sets, higher transcript level of DPYD and
lower levels of PPAT, UMPS, RRM2, and SLC29A1 were established in
tumors compared to paired adjacent mucosa tissues. RRM2
downregulation significantly associated with poor response of
patients to the first-line palliative treatment by 5-FU in testing
set and this was confirmed by survival analysis of the validation
set. Strong methylation of UPP2, but no transcript levels were
found in both tumor and control tissues. DPYS was significantly
more methylated in tumors in comparison with adjacent mucosas of
testing and validation sets. Low intratumoral UPB1 methylation
levels predicted poor disease-free interval in both sets of
patients. Most of the investigated 5-FU pathway genes showed no
methylation in either tumor or adjacent mucosa tissues.